1. Field of the Invention
The invention relates to a projection screen.
2. Description of the Related Art
A projection display is also called as rear-projection display and its example is illustrated in FIG. 1. As shown in the FIG. 1, the projection display 1 injects light from a light source unit 3 on a mirror 6 through an image display unit 4 and then projection lens 5, and the light coming through the image display and the projection lens is reflected on the mirror to project an image on a screen 7 from a rear face. A liquid crystal panel, a cathode ray tube (CRT) and the like are used for the image display unit 4. Further, there is also a system of directly projecting an image from the image display unit on a screen.
A combination of Fresnel lenses and lenticular lenses is usually used for the screen 7 of such projection display. The Fresnel lenses have a function of converting light from a light source or a mirror to parallel light and injecting light nearly vertical to the lenticular lenses. On the other hand, the lenticular lenses have a function of controlling and scattering light injected from the Fresnel lenses.
As the material of the Fresnel lenses and lenticular lenses for the projection screen, transparent thermoplastic resins such as an acryl resin, a polystyrene resin, a polyvinyl chloride resin and a polycarbonate resin can be used. Among these, the acryl resin is preferably used in view of its transparency, hardness, durability, processing suitability and the like. Further, those to which light diffusion was imparted by mixing light diffusion materials such as silica, alumina, clay, glass and beads to the above-mentioned thermoplastic resin are widely used for the lenticular lenses.
Both of light diffusion performance and light transmission performance are important in the projection screen. Although a conventional projection screen is superior in light diffusion, total light transmittance is low; therefore a screen becomes dark. When the total light transmittance is increased for making the image projected on a screen bright, the light diffusion and the resolution of the image on a screen is lowered; therefore it has been desired to simultaneously satisfy both of light diffusion performance and light transmission performance. Further, a conventional projection screen has had moiré patterns caused by the pitches of the Fresnel lenses and lenticular lenses are often appeared on a screen. Further, since an angle range providing an image with a high level visibility was narrow, a conventional screen was not satisfactory as a screen used for a large-sized television with a high-level image quality.
In order to improve above, several methods by which a light control film having the dependency of haze value on an angle is applied to the projection screen are proposed. For example, it is described in Japanese Patent No. 2838295 that alight control film having the dependency of haze value on an angle which was obtained by curing a composition having at least two kinds of optically polymerizable monomers or oligomers which have different refractive indices by irradiating light from two directions or more is used as the projection screen. Further, it is described in Japanese Patent Publication No. H4-77728 A that a plural number of light control films having the dependency of haze value on an angle which were obtained by curing a composition having at least two kinds of optically polymerizable monomers or oligomers which have different refractive indices by irradiating light are laminated and are used as the projection screen.
When the light control films proposed by these literatures are used to the projection screen, a bright image on the screen can be obtained while keeping total light high transmittance. However, such screen dose not necessarily satisfy the desire that an image with a high level quality is provided over a wide angle range as a large-sized television.
Further, a method of preparing a light control film having the dependency of haze value on an angle which was obtained by forming a film from a composition having at least two kinds of optically polymerizable monomers or oligomers which have different refractive indices and curing it by irradiating light from a specific direction on it, and a composition thereof are described, for example, in Japanese Patent Publication No. H07-58361 B; Japanese Patent No. 2691543, No. 2702521, No. 2782200, No. 2782250, No. 2822065, No. 3211381 and the like.